Apparently, the game's profile says it is a fangame, but it really isn't. It was put on the official Nintendo website and was developed by Nintendo themselves, so why does it say it's a fangame?

Unknown to many, Tetris DS got a promotional flash game around the time it came out. It's very short with 5 levels in the style of Tetris DS's Puzzle mode. I was able to get a time of 0:34.3, and I honestly think it could be improved.